The problem with Mechagnomes (and to a much lesser extent Earthen) is that they are direct Titan constructs. They don't have whatever it is that makes player character special enough (to the Titans and Old Gods) to be worth fighting for or against, those being said to be courage, resolve, and heroism . Earthen show signs of independence at least. Mechagnomes appear to be programmed constructs.
This is why I dismiss Mechagnomes. Junker Gnomes...cyborgs, would work however.